/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: HP
 * Date: 2022-04-27
 * Time: 16:55
 */
public class FindLonelyDog {
    public static void main(String[] args) {
        int num[]={4,5,6,5,4};
        int ret = 0;
        for (int i = 0; i < num.length; i++) {
            ret^=num[i];
        }
        System.out.println(ret);
    }
}
